1. Field of the Invention
The present invention relates to an electromechanical conversion element, a manufacturing method thereof, a piezoelectric type actuator, a liquid droplet jetting head, and an inkjet recording apparatus.
2. Description of the Related Art
In relation to an inkjet recording apparatus and a liquid droplet jetting head used as an image recording apparatus or an image forming apparatus such as a printer, a fax machine, and a copier, there is known a device with a nozzle for jetting ink droplets, a pressure chamber to which the nozzle is connected, and an electromechanical conversion element such as a piezoelectric element for applying pressure to the ink inside the pressure chamber.
For example, the electromechanical conversion element has a structure in which an electromechanical conversion film is disposed between a bottom electrode and a top electrode. The conventional technology discloses a method of forming an electromechanical conversion film with good crystalline orientation properties. Specifically, a noble metal electrode including titanium on which the titanium has been deposited in island shapes on the surface is used as the bottom electrode, and an electromechanical conversion film is formed on this metal electrode. Furthermore, there are cases where a platinum film and a conductive oxide film are sequentially formed on a titanium film by a sputtering method to form the bottom electrode, and a film made of lead zirconate titanate (PZT) is formed as an electromechanical conversion film on the conductive oxide film.
However, when forming a platinum film and a conductive oxide film on a titanium film by a sputtering method, the temperature needs to be high. Therefore, the titanium diffuses in the platinum film, and holes are formed in the platinum film.
If holes are formed in the platinum film, the continuity of the conductive oxide crystal in the conductive oxide film is hampered by the holes. Therefore, it becomes difficult to make the conductive oxide film have a higher average particle diameter than the platinum film, and the surface of the conductive oxide film becomes rough. As a result, an electromechanical conversion having good crystalline orientation properties cannot be formed.
Furthermore, the lead component of PZT constituting the electromechanical conversion film excessively diffuses on the rough parts of the surface of the conductive oxide film and in the holes in the platinum layer. Thus, a leak path is formed and electric field concentration occurs, and the withstand voltage of the electromechanical conversion element decreases.
By increasing the thickness of the platinum film, holes can be eliminated. However, this is not desirable because increasing the thickness of the platinum film, which is an expensive metal, incurs an increase in cost. Similarly, by reducing the thickness of the titanium film, it is possible to reduce the amount of titanium diffusing in the platinum film. However, if the thickness of the titanium film is excessively reduced, the adhesion between the platinum film and the vibrating plate on which the titanium film is formed is deteriorated, and peeling occurs in the bottom electrode.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-186646